Method for improvement of electromigration of copper by carbon doping

Abstract

A method for forming a carbon doped copper layer, preferably an electrochemically deposited carbon doped copper layer over a semiconductor structure, comprising the following steps. A semiconductor structure having an upper surface is provided. The semiconductor structure is placed in an electrochemical bath having a predetermined concentration of carbon. A first carbon doped copper layer is electrochemically deposited for a first period of time at a first current density. The first carbon doped copper layer blanket fills the semiconductor structure and has a predetermined thickness and a first concentration of carbon. A second carbon doped copper layer is electrochemically deposited over the first carbon doped copper layer for a second period of time at a second current density. The second carbon doped copper layer has a predetermined thickness and a second concentration of carbon. The carbon doped copper layer formed by the process of the present invention has improved electromigration without causing high resistivity.

We claim: 
     
       1. A method for forming a carbon doped copper layer, the steps comprising: providing a semiconductor structure having an upper surface;   placing said semiconductor structure in an electrochemical bath having a predetermined concentration of carbon;   electrochemically depositing a first carbon doped copper layer for a first period of time at a first current density; said first carbon doped copper layer having a predetermined thickness and a first concentration of carbon; said first carbon doped copper layer blanket filling said semiconductor structure upper surface; and   electrochemically depositing over said first carbon doped copper layer a second carbon doped copper layer for a second period of time at a second current density; said second carbon doped copper layer having a predetermined thickness and a second concentration of carbon.   
     
     
       2. The method of claim 1, wherein said first concentration of carbon in said first carbon doped copper layer is higher than said second concentration of carbon in said second carbon doped copper layer. 
     
     
       3. The method of claim 1, wherein said first current density is lower than said second current density. 
     
     
       4. The method of claim 1, wherein said predetermined concentration of carbon in said electrochemical bath is inversely proportional to said first and second current densities. 
     
     
       5. The method of claim 1, wherein said first period of time is from about 5 seconds to 300 seconds, and said second period of time is from about 30 seconds to 400 seconds. 
     
     
       6. The method of claim 1, wherein said first period of time is from about 10 seconds to 120 seconds, and said second period of time is from about 120 seconds to 290 seconds. 
     
     
       7. The method of claim 1, wherein said predetermined thickness of said first carbon doped copper layer is from about 550 to 4000 Å and said predetermined thickness of said second carbon doped copper layer is from about 2000 to 15,000 Å. 
     
     
       8. The method of claim 1, wherein said first current density is from about 1 to 30 milliamps/cm 2  and said first concentration of carbon in said first carbon doped copper layer is from about 0.1 wt. % to 3 wt. %, and said second current density is from about 10 to 35 milliamps/cm 2  and said second concentration of carbon in said second carbon doped copper layer is from about 0.01 wt. % to 1 wt. %. 
     
     
       9. The method of claim 1, wherein the ratio of said second current density to said first current density is from about 2 to 10. 
     
     
       10. The method of claim 1, wherein the ratio of said second current density to said first current density is from about 4 to 6. 
     
     
       11. The method of claim 1 further including the step of planarizing said second carbon doped copper layer. 
     
     
       12. A method for forming a carbon doped copper layer in a trench, the steps comprising: providing a semiconductor structure and a trench formed therein; said semiconductor structure having an upper surface;   placing said semiconductor structure in an electrochemical bath having a predetermined concentration of carbon;   electrochemically depositing a first carbon doped copper layer for a first period of time at a first current density; said first carbon doped copper layer having a predetermined thickness and a first concentration of carbon; said first carbon doped copper layer blanket filling said semiconductor structure upper surface; and   electrochemically depositing over said first carbon doped copper layer a second carbon doped copper layer for a second period of time at a second current density; said second carbon doped copper layer having a predetermined thickness and a second concentration of carbon.   
     
     
       13. The method of claim 12, wherein said first concentration of carbon in said first carbon doped copper layer is higher than said second concentration of carbon in said second carbon doped copper layer. 
     
     
       14. The method of claim 12, wherein said first current density is lower than said second current density. 
     
     
       15. The method of claim 12, wherein said trenched semiconductor structure includes a barrier layer lining said semiconductor structure upper surface and said within said trench; said barrier layer being selected from the group tantalum nitride, titanium nitride, titanium--tungsten, and nitrided--titanium--tungsten. 
     
     
       16. The method of claim 12, wherein said first period of time is from about 5 seconds to 300 seconds, and said second period of time is from about 30 seconds to 400 seconds. 
     
     
       17. The method of claim 12, wherein said first period of time is from about 10 seconds to 120 seconds, and said second period of time is from about 120 seconds to 290 seconds. 
     
     
       18. The method of claim 12, wherein said predetermined thickness of said first carbon doped copper layer is from about 300 to 700 Å and said predetermined thickness of said second carbon doped copper layer is from about 4000 to 6000 Å. 
     
     
       19. The method of claim 12, wherein said first current density is from about 1 to 5 milliamps/cm 2  and said first concentration of carbon in said first carbon doped copper layer is from about 0.1 wt. % to 1 wt. %, and said second current density is from about 20 to 25 milliamps/cm 2  and said second concentration of carbon in said second carbon doped copper layer is from about 0.01 wt. % to 0.1 wt. %. 
     
     
       20. The method of claim 12, wherein the ratio of said second current density to said first current density is from about 2 to 10. 
     
     
       21. The method of claim 12, wherein the ratio of said second current density to said first current density is from about 4 to 6. 
     
     
       22. The method of claim 12 further including the step of planarizing said second carbon doped copper layer to form a planarized copper filled trench.